Gear & Gadgets —

The Palm Pre’s possible Achilles heel: battery life

There are any number of glitches that could keep the Palm Pre from totally …

When the Palm Pre hits the streets sometime this year, geeks and ordinary mobile users alike will finally get to touch the magic, which is great, because we certainly weren't touching any magic at CES. We got to look, but Palm was pretty adamant about not letting anyone who wasn't a Palm employee get their mitts on it. This is understandable, because the demo units were clearly more "mock-up" than true "demo."

A lot—perhaps even the majority—of the Pre's functionality was missing or not working reliably, and many features were only "working" in the sense of "if I press these three buttons at once it triggers a fake incoming SMS from 'Jim Coworker' about that party on Friday." But we all went along with it, because those mockups were so great to look at. Nonetheless, the whole experience left me wondering, "so when this comes out, what are we going to realize is wrong with it?"

For reasons that I'll outline below, I'd like to suggest that the answer to the above question is a common one for a first-generation (or, in some cases, a second-generation) smartphone product: the battery life will disappoint many users.

Not your father's smartphone CPU

The 65nm TI OMAP3430 that powers the Pre is no joke--it's the kind of beefy media SoC that you'd expect to see in a portable media player, where you can pair it with a bigger battery. Indeed, it's used in the Archos 5, and some Googling turns up plenty of talk from the GP32X community about using it for one of their devices.

As you can see from the block diagram below, at the heart of the 3430 is an ARM Cortex A8 core, and in fact this SoC was actually the first to market with the A8 core back in 2006.

The Cortex A8 is ARM's post powerful in-order processor, with the even more powerful A9 boasting an out-of-order execution core that should significantly boost performance up into Atom territory, but at a significantly lower power draw.

From a very high level, the A8's microarchitecture is similar to that of the original Pentium, but an even better comparison is Intel's Atom. Both the A8 and Atom are dual-issue, in-order processors, each of which has two main integer pipelines and a separate pipeline for floating-point and SIMD. A8's integer pipeline is 13 stages (compare to Atom's 16 stages), which is quite long for an in-order part, but this helps the core to achieve higher clockspeeds.

There's no word on the official clockspeed of the Pre's SoC, but anything up to 1GHz is possible, though only a little over half that speed is more likely given power constraints.

A8 also has support for a wide variety of SIMD instructions, and in general it is a full-featured, modern core on the order of Intel's Atom. In this respect, A8 is a huge departure from previous ARM cores, all of which were single-issue and not superscalar.

The A8 is paired with a PowerVR GPU and a very nice array of DSP and I/O blocks, which I won't enumerate here because they're clearly marked in the diagram above. These blocks alone would make it a very capable media portable, but it's the A8 core that gives the 3430 the horsepower to run the Pre's rather demanding software stack. (More on the this stack below.)

Right now, no one knows what the power draw is for the Pre's 3430, because the device's clockspeed hasn't been made public. We also don't know how many other chips that Palm has packed in there with it.

But my point in talking about the capabilities of the A8 is that, even though the 3430 is a 65nm part, you don't get all of that hardware for nothing. The radio and the screen will be the biggest power draws in the Pre, but 3430 will definitely contribute its fair share when the SoC is under load and the 3430's considerable dynamic power management features are more constrained in scaling back the core frequency or cutting power to one of the 16 different power domains.